The present invention relates to an electromagnetic sliding shoe brake comprising a brake shoe which is pulled against a ferromagnetic take-up member for applying a predetermined brake force to the take-up member. Such ferromagnetic take-up member may, for example, be a rail when this type of brake is installed in or on a rail vehicle.
Such a brake is, for example, necessary where it is not possible to apply a sufficient brake force to a rail vehicle solely by means of the brake force applied to the wheels to thereby achieve a sufficient deceleration for example in an emergency. In such situations it is conventional to generate additional braking forces by means of a sliding shoe brake also referred to as a slipper shoe brake. Such additional brake forces are produced by friction between the brake or slipper shoe and the top surface of the rail caused by corresponding electromagnetic attraction forces between the sliding shoe and the rail. In such a use the electromagnetic slide shoe brake actually functions as an emergency brake which must satisfy several requirements. On the one hand an emergency brake must assure the application of a certain minimum brake force. Normally, such minimum brake force is larger than the maximum brake force applied to the rail vehicle by the service brake such as an electrical service brake of the rail vehicle. On the other hand, it is required that the maximum brake force of the emergency brake or of the sliding shoe brake is only insignificantly larger than its minimum brake force. However, this minimum brake force must be determined in accordance with a minimum friction coefficient between the sliding shoe and the rail in order to achieve the minimum brake force which is required for obtaining the necessary deceleration of the rail vehicle for any friction coefficient. As a result, the normally present friction coefficients are at least four times larger than the minimal friction coefficient, whereby correspondingly larger brake forces are caused. These larger brake forces result in a respectively larger, undesired vehicle deceleration which substantially reduce the passenger safety. Additionally, these undesirably large decelerations result in an unnecessarily large loading of the rail track body or of the roadway or roadbed.
Heretofore, such loading of the rail track or roadbed required meeting, among other conditions, the condition that the road construction is over-dimensioned. The over-dimensioning of the track was especially required for elevated tracks which are capable of taking up longitudinal loads only to a limited extent. Such over-dimensioning was necessary heretofore especially for tracks constructed for high speed vehicles, for example, magnetic levitation vehicles.
In view of the foregoing it is clear that a sliding shoe brake which is designed to meet the first requirement, namely to provide a certain minimum braking force, will not satisfy the second requirement that the maximum braking force resulting from normal frictional coefficients will not be substantially larger than the minimum braking force so that vehicle decelerations will always correspond to decelerations resulting from the application of the minimum braking force by the sliding shoe brake.